Blue Planet II - Coral Reefs

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Coral reefs occupy less than one tenth of one per cent of the ocean floor yet they are home to a quarter of all known marine species. They are complex, infinitely varied structures providing all kinds of homes for their many residents. As in any crowded metropolis, there is fierce rivalry for space, for food and for a partner. The broadclub cuttlefish has found its place in the city by using a hypnotic display that apparently mesmerises its prey, causing it to let down its defences and subsequently providing a meal. On the Great Barrier Reef we meet a remarkable grouper which uses sign language, dubbed the ‘headstand signal’, to reach out to an entirely different creature, a reef octopus, to flush small fish from their hiding holes and into the groupers waiting mouth. At night the reef becomes a dangerous place, as metre-long bobbit worms strike from their burrows.